Two powerful facets of humoral immunity are the ability to rapidly generate neutralizing antibodies to pathogens and pathogen-derived toxins, and to provide memory such that pathogen re-encounter will meet with a more swift and efficacious response. To accomplish these goals, naive B cells need to efficiently recognize antigen, elicit T cell help and undergo clonal expansion to achieve distinct cellular outcomes. Little is known, however, regarding the molecular cues that drive these distinct cellular fates. Herein we investigate the pivotal roles of SHIP and PTEN inositol phosphatases in regulating the PI3K pathway and its noted impact on late B cell maturation. In Aim 1, we address the role of PTEN in governing the bifurcative step towards plasma cell or germinal center B cell commitment. Parameters of antigen affinity and the contribution of CD40 signaling will be specifically addressed. These findings will be related to alterations in downstream signaling via the PI3K pathway, as well as the transcription factor network that is known to regulate this stage of B cell differentiation. In Aim 2, we will perform similar studies to determine the role of SHIP phosphatase at this differentiative step. In addition, we will determine if SHIP possesses important physiologic functions that are independent of PI(3,4,5)P3 hydrolysis. In Aim 3, we will examine the roles of SHIP and PTEN within the germinal center microenvironment and in the memory B cell compartment. Novel approaches utilizing immunoglobulin knock-in mice, inducible B cell-specific gene targeting, conditional retroviral gene expression and germinal center B cell purification techniques enhance the feasibility and impact of these studies. PUBLIC HEALTH RELEVANCE: The efficacy of most vaccines depends upon the generation of high-affinity antibodies and long-lived memory B cells that rapidly differentiate into antibody producing cells upon pathogen re-exposure. We will examine the contribution of the PI3-kinase pathway to these processes in an effort to understand the molecular basis of these late stage B cell differentiation events. Such knowledge will be of direct relevance for the application of small molecular therapeutics to enhance (e.g. for vaccines) or inhibit (e.g. in autoimmunity) the PI3-kinase pathway in specific settings.